The present invention relates to an air-conditioner for a motor vehicle, especially one having a compressor arranged in a refrigerant circuit and an evaporator for the cooling of air to be conditioned for the passenger compartment. More particularly, the present invention relates to such air-conditioning systems that embody a cold storage medium.
Motor vehicle manufacturers are striving to reduce the fuel consumption of their vehicles. One measure for reducing the fuel consumption is to cut off the engine while at a temporary standstill, such as when stopping at a traffic light, for example, or under other driving conditions, in which a drive power output of the engine is, at least temporarily, not needed. This temporary engine cut-off is also known as idle-stop mode. Such measures are already at least partially used in present-day fuel-saving vehicles, such as the so-called “three-liter” vehicle, for example. In vehicles having the idle-stop operating mode, the engine is shut off for approximately 25-30% of the journey time in urban traffic.
This is one reason why such vehicles are not equipped with an air-conditioner. With the engine shut off, the compressor essential to an air-conditioner cannot be powered either, and therefore in the idle-stop mode an air-conditioner cannot provide the necessary refrigeration capacity.
To solve this problem it is proposed in EP 0 995 621 A2 to use the condensate produced in the cooling of moist air to ice-up the evaporator of the air-conditioner, so that in the idle-stop mode, when the engine is shut off, the air can be cooled by the then melting ice. This method has numerous disadvantages, however. The quantity of water that is present in the air and is needed for icing-up of the evaporator varies as a function of the ambient climatic conditions. Thus, it may happen that, with low air humidity there is insufficient condensation water available to ice-up the evaporator. Furthermore, a relatively long, period of time is generally needed for icing-up of the evaporator, so that this known air-conditioner can function in idle-stop mode only after a relatively long driving time. Another problem is that the evaporator generally ices-up unevenly, so that the evaporator has some areas that are iced-up and some areas that are not. Furthermore, icing may be so intense that the air can flow through the evaporator only with a high pressure loss, if at all. In any case, the layer of ice produces a pressure loss on the air side, which leads to the need for an increased blower output.